The invention relates generally to electric vehicles, and more specifically to the use of a modular internal combustion engine as an auxiliary power unit (APU) for hybrid electric vehicles (HEVs).
Purely electric vehicles typically use stored electrical energy to power an electric motor, which propels the vehicle. Electric vehicles have an intrinsic problem of energy storage, and consequently have a limited driving range. Therefore, APUs are needed to generate additional electricity to the electric vehicle's power system. These APUs both supply a secondary source of energy to the vehicle as needed and recharge the vehicle's primary energy source. Because these APUs are intended to continuously recharge the primary energy source of the electric vehicle, they must be rated according to the vehicle's average power demand.
Traditionally, conventional combustion engines or turbines are used to generate the necessary auxiliary or secondary power. However, both options have drawbacks associated therewith respect to vehicle power generation, thus lowering the effectiveness of the APU. That is, to be effective as an auxiliary power source, it is desirable that the APU have a high efficiency, high reliability, low complexity, and small volume. Conventional combustion engines are overly complex for use as APUs because both the starter and crankshaft are not needed for the generation of electric power. Turbines, on the other hand, have a very low efficiency because the power they generate is often scaled down for use in the electric vehicle.
Therefore, it would be desirable to have an APU assembly capable of efficiently supplying auxiliary power to an electric motor. It would further be desirable to operate the APU assembly in a fashion that optimizes efficiency thereof.